Control device for starting fuel cell vehicle

ABSTRACT

A control device for starting a fuel cell is provided which is capable of preventing an excessive reduction of the terminal voltage of the fuel cell. A primary precharge portion, provided with a high voltage switch and a current limiter, is disposed at the output portion of a power storage unit, and a secondary precharge portion, provided with a DC-DC chopper and a control portion, is disposed at the output side of a fuel cell. The primary precharge portion controls the output current to flow in a path via a resistor having a predetermined resistance. The secondary precharge portion controls an output current of the fuel cell based on a current command value IFCCMD for the fuel cell.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a control device for starting a fuelcell vehicle, and in particular, relates to a technique for starting thefuel cell in a hybrid-type power source device provided with a powerstorage unit for assisting a power supply from the fuel cell.

2. Description of the Related Art

Conventionally, a hybrid-type fuel cell power generation system isknown, which comprises a fuel cell and a power storage unit such as abattery or a capacitor (electric double layer capacitor or condenser) inorder to compensate the output responsiveness of the fuel cell, which isdriven by a fuel gas supply. The fuel cell vehicle is installed with asolid polymer-type fuel cell, which is composed of a plurality of cells,each of which is formed by sandwiching a solid polymer electrolytemembrane corresponding to a solid polymer ion exchange membrane betweenan anode and a cathode.

In the above conventional hybrid-type fuel cell power generation system,when starting the fuel cell, first, air is supplied to a pressurecontrol valve at the fuel side, for example, and fuel gas is supplied tothe fuel electrode in response to air pressure supplied to the pressurecontrol valve.

Thus, before starting the fuel cell, the power storage unit supplieselectric driving power to the compressor which supplies air. In additionto auxiliary devices for driving the fuel cell, the power storage unitsupplies electric power to the motor for driving the vehicle when thevehicle starts immediately after the start of the fuel cell, so that thepower stored in the power storage unit is reduced, and the voltagebetween both terminals of the power storage unit is reduced.

When the fuel cell is connected to the power storage unit, whose voltagebetween both terminals has been reduced, a large current rapidly flowsfrom the fuel cell to the power storage unit. In the course oftranslating the voltage between both terminals of the fuel cell and thepower storage unit into a balanced state, the voltage between bothterminals of the fuel cell is reduced. Then, the fuel cell is in dangerof losing hydrogen or the water content in the solid polymer electrolytefilm, or of experiencing a decrease in the durability of the fuel cell.

As described above, if the fuel cell is connected to the capacitor undera condition that the terminal voltage of the capacitor greatly differsfrom the terminal voltage of the fuel cell (output voltage of the fuelcell) at the time, for example, of starting the fuel cell, a largecurrent may flow, which may cause a danger that the performance or thedurability of the fuel cell will become deteriorated.

SUMMARY OF THE INVENTION

In the conventional fuel cell power source device, when the fuel cell isbeing started, air is first supplied to the pressure control valve forsupplying fuel, and fuel supply is started in response to the airpressure supplied to the pressure control valve.

Thus, prior to activation of the fuel cell, a driving electric power issupplied to the fuel supply device such as an air compressor. Inaddition to the activation of the fuel cell driving auxiliary machinesand various control devices, electric power is supplied from thecapacitor to the propulsion motor, which is driven immediately afterstarting the fuel cell vehicle, which results in reducing the capacitorenergy causing depression of the terminal voltage of the capacitor.

If the capacitor, in which terminal voltage has been depressed, and thefuel cell are connected, a large current flows from the fuel celltowards the capacitor, the terminal voltage of the fuel cell is reducedin the course of recovering both terminal voltages of the fuel cell andthe capacitor to an equilibrium voltage. When the terminal voltage ofthe fuel cell is depressed, the performance or the long-term stabilityof the fuel cell are in risk of being deteriorated, or hydrogen andwater in the solid polymer electrolyte membrane are in danger of beingevaporated.

As described above, when the fuel cell and the capacitor are connectedto each other under conditions that the terminal voltage of thecapacitor is far below the terminal voltage of the fuel cell, a largecurrent flows from the fuel cell to the capacitor, which may cause adanger to the performance and long-term stability of the fuel cell willbe deteriorated.

The present invention was made in order to solve the above problems andan object of the present invention is to provide a control device forstarting the fuel cell vehicle and which is capable of preventing anexcessive reduction of the voltage between both terminals of the fuelcell.

One aspect of the present invention provides a control apparatus forstarting a fuel cell vehicle comprising: a fuel cell (for example, afuel cell 11 in the embodiment) supplying electric power to a load (forexample, driving motor 13, PDU 14, and air compressor 15, etc. in theembodiment); a capacitor (for example, power storage unit 12 in theembodiment) for assisting the supply of electric power to the load andfor storing generated energy of the fuel cell; a fuel cell drivingdevice (for example, air compressor 15 in the embodiment) for supplyingreaction gases (for example, hydrogen gas and air in the embodiment) andfor driving the fuel cell; and a current limiting device (for example, asecondary precharge circuit 17 in the embodiment) for limiting an outputcurrent (for example, output current Ifc in the embodiment) from thefuel cell; wherein, at the time of starting the fuel cell, the capacitorsupplies electric energy to the fuel cell driving device and the currentlimiting device prohibits the fuel cell from outputting an outputcurrent until an output voltage (for example, output voltage Vfc in theembodiment) of the fuel cell reaches a predetermined voltage, and, afterthe output voltage rises to more than the predetermined voltage (forexample, V_(MOT)≈Vst≈Vfc in the embodiment), the current limiting devicelimits the output current of the fuel cell to below a predeterminedcurrent value until the difference between the output voltage of thefuel cell and a terminal voltage of the capacitor (for example, terminalvoltage Vst in the embodiment) reaches a predetermined voltagedifference (for example, predetermined voltage difference ΔV in theembodiment).

According to the above constitution of the control apparatus forstarting a fuel cell vehicle, since the output current of the fuel cellis limited at the time of starting the fuel cell, it is possible toprevent the terminal voltage of the fuel cell from reducing rapidly.

That is, at the time of starting the fuel cell, air is supplied to thepressure control device for supplying fuel to the fuel electrode of thefuel cell in addition to the air electrode of the fuel cell. In thiscase, the capacitor supplies electric power to the fuel cell drivingdevice and the terminal voltage of the capacitor reduces. By providing aprimary precharge circuit, which is provided with a resistor having arelatively high resistance, the capacitor can output a limited currentto the fuel cell driving device or the power drive unit of the drivingmotor through the resistor, to thereby prevent the fuel cell fromgenerating large output current.

In the above case, the DC-DC chopper prohibits the output currentflowing from the fuel cell until the output voltage of the fuel cellreaches a predetermined voltage, and, the DC-DC chopper limits theoutput current flowing from the fuel cell, even after the output voltageof the fuel cell has been reached to a predetermined voltage, thereby,it is possible for a large current to flow from the fuel cell to thecapacitor.

The above mechanism prevents a large current from flowing from the fuelcell to the capacitor until the voltage difference between the terminalvoltage of the fuel cell and the terminal voltage of the capacitorbecome less than a predetermined value. Thus, in that period, thecapacitor is gradually charged by a limited current from the fuel cell,and the terminal voltage of the capacitor approaches to the terminalvoltage of the fuel cell. Therefore, it is possible to preventevaporation of water or hydrogen from the solid polymer electrolytemembrane of the fuel cell and also to prevent the fuel cell from losinglong-term stability, which contributes to maintain the performance andlong-term stability.

By the use of the DC-DC chopper as a current limiting device, it becomespossible to control the output current of the fuel cell by changing aduty ratio of a pulse current which is input for controlling thechopping operation, and to reduce a time period until both terminalvoltages of the fuel cell and the capacitor attain an equilibrium whilepreventing a rapid drop of the terminal voltage of the fuel cell.

The second aspect of the present invention provides a fuel cell powersource system comprising: a fuel cell for supplying electric power to aload, an electric power storage device for assisting supply of electricpower to the load, and a switching device (for example, a DC-DC chopper17 a in the embodiment), disposed between the fuel cell and thecapacitor, for switching connection or disconnection of the fuel cellwith the capacitor; and a control device (for example, a control portion17 b in the embodiment) for controlling the switching device, whereinwhen the fuel cell is being connected to the capacitor, the controldevice detects the voltage difference between a terminal voltage of thecapacitor (for example, a terminal voltage of the capacitor Vst in theembodiment) and a terminal voltage of the fuel cell (for example, aterminal voltage of the fuel cell Vfc in the embodiment), when thevoltage difference is larger than a predetermined value, the controldevice executes a chopping control of the switching device.

The third aspect of the present invention provides a fuel cell powersource system comprising: a fuel cell for supplying electric power to aload, a capacitor for assisting supply of electric power to the load, aconnecting device (for example, a DC-DC chopper 17 a and a currentlimiting device 16 b in the embodiment), disposed between an output endof the fuel cell and the capacitor, for connecting an output end of thefuel cell and the capacitor, and a control device (for example, acontrol device 17 b and a fuel cell control device 32 in the embodiment)for controlling the connecting device as to whether the fuel cell isconnected or disconnected with the capacitor, wherein when the fuel cellis being connected to the capacitor, the control device detects thevoltage difference between the terminal voltage of the fuel cell (forexample, a terminal voltage of the fuel cell Vfc in the embodiment) andthe terminal voltage of the capacitor (for example, a terminal voltageof the capacitor Vst in the embodiment), and when the voltage differenceis larger than a predetermined value, the control device controls theconnecting device so as to limit an amount of a current (for example, anoutput current Ifc in the embodiment) flowing from the fuel cell to thecapacitor.

The fourth aspect of the present invention provides the fuel cell powersource system, wherein the control device connects the fuel to thecapacitor after the fuel cell has been activated.

The fifth aspect of the present invention provides a fuel cell powersource system which comprises a control device comprising a primaryprecharge circuit (for example, a primary precharge circuit 16 in theembodiment), disposed downstream of the capacitor, comprising aswitching device (for example, a switching device 16 a in theembodiment) and a current limiting device (for example, a currentlimiting device 16 b in the embodiment), and a secondary prechargecircuit (for example, a secondary precharge circuit 17 in theembodiment), disposed downstream of the fuel cell, comprising a choppingdevice (for example, a DC-DC chopping device 17 a in the embodiment) anda chopper control device (for example, a chopper control device 17 b inthe embodiment), wherein when the voltage difference between theterminal voltage of the fuel cell and the terminal voltage of thecapacitor exceeds a predetermined value, the current limiting device ofthe primary precharge circuit and the DC-DC chopper of the secondaryprecharge circuit control an amount of current flowing from the fuelcell flowing to the capacitor, and when a voltage difference between theterminal voltage of the fuel cell and the terminal voltage of thecapacitor is reduced below the predetermined value, the primaryprecharge circuit and the secondary precharge circuit allow currentflowing from the fuel cell to the capacitor and to the load.

As shown in FIG. 3, the control apparatus includes a DC-DC chopper 17 a,in which ON/OFF of the transistor TR is controlled by supplying a pulsecurrent to the base of the transistor. The control device 17 b changesthe duty ratio of the pulse current (the ratio of ON/OFF) so as toextend the OFF state of the transistor.

The sixth aspect of the present invention provides a method forcontrolling start of a fuel cell vehicle, the fuel cell having a fuelcell provided with a fuel cell driving device for supplying electricpower to a load, an electric power storage device for assisting supplyof electric power to the load, the control apparatus for controlling thefuel cell power source system having a primary precharge circuitdisposed downstream of the capacitor, comprising a switching device anda current limiting device; and a secondary precharge circuit disposeddownstream of the capacitor, comprising a DC-DC chopper and a choppercontrol device, the control method comprising the steps of opening theswitching device of the primary precharge circuit when the terminalvoltage of the capacitor and the terminal voltage of the load reach anequilibrium voltage after supplying a limited current from the capacitorthrough the current limiting device (for example, a current limitingdevice 16 b in the embodiment), activating the fuel cell by activatingthe fuel cell driving device by supplying fuel to the fuel cell,detecting a voltage difference between the terminal voltage of the fuelcell and the terminal voltage of the capacitor, executing a choppingcontrol of the output current of the fuel cell by the DC-DC chopper whenthe voltage difference exceeds a predetermined value when the voltagedifference is reduced to be less than a predetermined value, andsupplying the output current from the fuel cell to the load when thevoltage difference is reduced below a predetermined value.

The seventh aspect of the present invention provides a method ofcontrolling a fuel cell power source system, the fuel cell power sourcesystem having a fuel cell provided with a fuel cell driving device forsupplying electric power to a load, a capacitor for assisting supply ofelectric power to a load including a driving motor, and a controlapparatus for controlling the fuel cell power source system having aprimary precharge circuit disposed downstream of the capacitor,comprising a switching device and a current limiting device; and asecondary precharge circuit disposed downstream of the capacitor,comprising a DC-DC chopper and a chopper control device, wherein thecontrol method comprises the steps of detecting a voltage differencebetween a terminal voltage of the capacitor and a terminal voltage ofthe fuel cell, limiting the output current of the fuel cell by the DC-DCchopper of the secondary precharge circuit when the voltage differenceexceeds a predetermined value, and opening the secondary prechargecircuit to supply the output current from the fuel cell to the capacitorand to the load when the second voltage difference reduces to be lessthan a second predetermined difference.

The fuel cell control device 32 outputs a rotation number command valueN as the driving order to the auxiliary devices and also controls theprimary and secondary precharge circuits 16 and 17, and controls thecontact points of relays provided at the high voltage switch 16 a andcurrent limiting device 16 in the primary precharge circuit 16 and alsooutputs the current command value IFCCMD as the switching command forthe chopper 17 so as to make the DC-DC chopper in the secondaryprecharge circuit execute the chopping control of the output current.This chopping control of the output current controls the time period forthe terminal voltages of both the capacitor and the fuel cell to reachan equilibrium. Moreover, the chopping control by the DC-DC choppereasily limits the current generated by the fuel cell by changing theduty ratio of the pulse current, so that it is possible to reduce thetime period until both terminal voltages of the fuel cell and thecapacitor reach an equilibrium voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the structure of a fuel cell vehicleprovided with a control device for starting the fuel cell vehicle.

FIG. 2 is a diagram showing the main structure of a control device forstarting the fuel cell vehicle shown in FIG. 1.

FIG. 3 is a diagram showing a constitution of a DC-DC chopper.

FIG. 4 is a flowchart showing the operation of the control device forstarting the fuel cell vehicle shown in FIG. 1.

FIG. 5 is a graph showing the time-dependent change of an output voltageVfc and an output current Ifc of the fuel cell, a terminal voltage Vstof the power storage unit, and a connection flag of the high voltageswitch.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, an embodiment of a control device for starting the fuelcell vehicle is described with reference to the attached drawings. FIG.1 is a diagram showing the structure of a fuel cell vehicle providedwith a control device for starting the fuel cell vehicle. FIG. 2 is adiagram showing the main structure of a control device for starting thefuel cell vehicle shown in FIG. 1. FIG. 3 is a diagram showing aconstitution of a DC-DC chopper.

A fuel cell vehicle 1 of this embodiment is provided with a hybrid-typepower source device including a fuel cell 11 and a power storage unit12, and a driving motor 13 for driving the vehicle generates drivingpower by receiving energy from the power source device; the drivingpower generated by the motor is transmitted to the driving wheelsthrough a transmission T/M, which is constituted by either one of anautomatic transmission or a manual transmission. When the driving poweris transmitted from the driving wheels to the driving motor 13 duringdeceleration of the fuel cell vehicle, the driving motor acts as agenerator and generates what is called regenerative braking power, andthe kinetic energy of the vehicle is recovered as electric energy.

A control device 10 for starting the fuel cell vehicle according to thepresent embodiment comprises, for example, a fuel cell 11, a powerstorage unit 12, a driving motor 13, a PDU (Power Drive Unit) 14, an aircompressor 15 as one of the auxiliary devices of the fuel cell, aprimary precharge portion 16, a secondary precharge portion 17, and anECU 18.

The driving motor 13 is formed of a permanent magnet type three-phase AC(alternating current) motor utilizing, for example, a permanent magnetas a field system, and the driving motor is controlled by three-phase ACpower supplied by the PDU 14.

The PDU 14 is provided with a PWM inverter constituted by a switchingelement such as an IGBT and the like, and the PDU 14 converts a DCvoltage output from the fuel cell 11 and the power storage unit 12 intothree-phase AC power to be supplied to the driving motor 13.

The fuel cell 11 is constituted by a stack of cells, each of which isformed by sandwiching both side surfaces of a solid polymer electrolytefilm between an anode and a cathode, and the fuel cell comprises ahydrogen electrode, to which hydrogen is supplied as a fuel, and an airelectrode, to which air containing oxygen as an oxidizing agent issupplied. The fuel cell 11 is constituted such that hydrogen ions,generated by a catalytic reaction at the anode, pass the solid polymerelectrolyte film and reach the cathode, wherein the hydrogen ionsgenerate electric power by an electrochemical reaction with oxygen.

A fuel supply portion 21 connected to the fuel electrode side of thefuel cell 11 comprises a pressure control portion 22 for supplyinghydrogen gas at air pressure in response to a control signal output fromthe ECU 18 or in response to air pressure supplied from an aircompressor 15 as a signal pressure.

The air compressor 15 connected to the air electrode side of the fuelcell 11 not only supplies air to the air electrode, but also suppliesair as a signal pressure for the pressure control portion 22 constitutedby a pressure flow control valve. In order to execute the aboveoperation, a number of rotations command value N of the motor forcontrolling the number of rotations of the motor, which drives the aircompressor 15, is input into a control portion 23 of the air compressor15.

The power storage unit 12 is a capacitor such as an electricdouble-layer capacitor or an electrolytic capacitor. In addition, thefuel cell 11 and the power storage unit 12 are connected in parallel tothe driving motor 13, which constitutes an electric load.

FIG. 2 is a diagram showing the main structure of a control device forstarting the fuel cell vehicle shown in FIG. 1. The control device isused to prevent an excessive reduction of the terminal voltage of thefuel cell at the time of starting the fuel cell.

A primary precharge portion 16 is disposed at the output side of thepower storage unit 12, and a secondary precharge portion 17 is disposedat the output side of the fuel cell 11.

As shown in FIG. 2, the primary precharge portion 16 is constituted by ahigh voltage switch 16 a and a current limiter 16 b, and when thecurrent to be supplied to the electric load such as the driving motor 13becomes large, then the high voltage switch 16 a is released, and thecurrent is made to flow through a resistor 16 c having a predeterminedresistance by closing the current limiter 16 b.

Thus, the high voltage switch 16 a is provided with relays, which areconnected to the respective output terminals of the positive andnegative electrodes and are controlled by a control signal output fromthe ECU 18 for opening and closing the high voltage switch 16 a.

The current limiter 16 b is provided with relays, which are connected inparallel to the high voltage switch 16 a and which are also connected torespective output terminals of the positive and negative electrodes, anda resistor 16 c with a predetermined resistance, so that the currentoutput from the power storage unit 12 is supplied to the PDU 14 throughthe resistor 16 c.

The secondary precharge portion 17 is constituted by a DC-DC chopper 17a and a control portion 17 b, and controls the output current Ifc fromthe fuel cell 11 based on the current command value IFCCMD, that is, thegeneration command to the fuel cell 11.

As shown in FIG. 3, the DC-DC chopper 17 a controls the ON/OFF operationof a transistor TR by supplying a pulse current to the base of thetransistor TR from the control portion 17 b, for example. The controlportion 17 b controls the output current by changing the duty ratio ofthe pulse current such that the OFF state of the transistor TR becomeslonger with an increase in the output current.

Note that a diode is disposed between the primary charge portion 16 andthe secondary charge portion 17 in order to prevent a countercurrentfrom flowing from the power storage unit 12 to the fuel cell 11.

In addition, as shown in FIG. 1, the control portion 23 of the aircompressor 15, in addition to the PDU 14, is connected in parallel tothe fuel cell through the secondary precharge portion 17.

A 12-V auxiliary battery 24 for driving various control devices of thefuel cell vehicles and accessory devices is provided with a DC-DCconverter 25, for example, which charges the auxiliary battery 24 afterreducing the DC voltage supplied from the fuel cell through thesecondary precharge portion 17.

In addition, a control device 27 of a motor 26 for driving the airconditioner is connected in parallel with the fuel cell 11 through thesecondary precharge portion 17, and the control device 27 converts DCelectric power output from the fuel cell 11 and the power storage unit12 into AC power to be supplied to the motor 26.

The ECU 18 is constituted by a motor ECU 31, a fuel cell control portion32, and a power storage unit control portion 33, for example.

The motor ECU 31 controls the power conversion operation of the PWMinverter provided in the PDU 14, and outputs switching commands such asa U phase AC voltage command value *Vu, a V phase AC voltage commandvalue *Vv, and a W phase AC voltage command value *Vw. The motor ECU 31then makes the PDU 14 output a U phase current lu, a V-phase current lv,and a W-phase current lw in response to these voltage command values*Vu, *Vv, and *Vw to respective phases of the driving motor 11.

The motor ECU 31 accepts various input signals, such as a signal of anaccelerator operational amount θTh related to an amount of depression ofthe accelerator by the driver, for example, a signal of a magnetic poleposition (electric angle) output from an angular velocity detector 35provided in the driving motor for detecting the magnetic pole position,signals of the respective phase currents lu, lv, and lw supplied fromthe PDU 14 to the driving motor 11, a signal of a motor current Imotoras a DC current component, and a signal of a supply voltage Vdc-insupplied to the PDU 14.

The fuel cell control portion 32 outputs the number of rotation commandvalue N as a command for driving the auxiliary devices for driving thefuel cell such as the air compressor 15, and also controls theoperations of the primary and secondary precharge portions 16 and 17.That is, the fuel cell control portion 32 controls the operations of thecontact points of relays arranged in the high voltage switch 16 a andthe current controller 16 b of the primary precharge portion 16. Thefuel cell control portion 32 also outputs a current command value IFCCMDto the DC-DC chopper 17 a of the secondary precharge portion 17 as aswitching command.

The fuel cell control portion 32 accepts various input signals, such asa signal of an output request value *P for the driving motor 13 and anoutput value P from the driving motor 13, a signal of a motor currentIs/c of a motor for driving the air compressor 15 output from thecontrol portion 23, a signal of the output current Ifc and outputvoltage Vfc from the fuel cell 11, both output from the secondaryprecharge portion 17, a DC voltage signal output from the DC-DC chopper17 a of the secondary precharge portion 17, and a signal of an outputcurrent value Iout Total output from a current detector 36 disposedbetween the primary and secondary recharge portions 16 and 17.

The power storage unit control portion 33 calculates the state of charge(SOC) of the power storage unit 12, for example, and outputs thecalculation results to the motor ECU 31 and the fuel cell controlportion 32.

In order to execute the above operation, the power storage unit 33accepts signals such as signals with respect to an output current Ist, avoltage Vst between terminals, and a temperature of the power storageunit 12.

That is, as shown in FIG. 2, the ECU 18, which controls the currentlimiting control of the primary and secondary precharge portions 16 and17, accepts various signals such as a signal from a first currentdetector 41 which detects the output current Ist from the power storageunit 12, a signal from a first voltage detector 42 for detecting theterminal voltage Vst between the terminals of the power storage unit 12,a signal from a second current detector 43 for detecting an outputcurrent Ifc from the fuel cell 11, a signal from a second voltagedetector 44 for detecting an output voltage Vfc of the fuel cell 11, anda signal from a third voltage detector 45 for detecting a motor voltageV_(MOT) of the driving motor 13.

The control device 10 for starting the fuel cell vehicle according tothe present embodiment is constituted as described above, and theoperations of the control device for starting the fuel cell vehicle,particularly the current limiting control of the primary and secondaryprecharge portions 16 and 17 are explained below with reference to theattached drawings.

FIG. 4 is a flowchart showing the operation of the start control device10 of the fuel cell vehicle, and FIG. 5 is a graph showing changes ofthe output voltage Vfc and the output current Ifc of the fuel cell 11,and the terminal voltage Vst of the power storage unit 12 and theconnection flag of the high voltage switch 16 a.

For example, at the time of starting the vehicle, the fuel cell 11, thepower storage unit 12, and the PDU 14 are disconnected from each other,so that the output voltage Vfc, the terminal voltage Vst, and the motorvoltage V_(MOT) show individual and different values.

First, in step S01 shown in FIG. 4, a current limiting control isperformed by the primary precharge portion 16. That is, the contactpoint of each relay of the high voltage switch 16 a is opened, and thecontact point of each relay in the current limiter 16 b is operated suchthat the current output from the power storage unit 12 is output througha resistor 16 c.

Subsequently, in step S02, the contact point of the high voltage switch16 a is actuated, after the motor voltage V_(MOT) and the terminalvoltage Vfc reach an equilibrium state, that is, a state whereV_(MOT)≈Vst≠Vfc.

Subsequently, in step S04, the fuel cell 11 is started. That is, the aircompressor 15 is started, which is used for supplying air not only tothe air electrode of the fuel cell 11 but also to the pressure controlportion 22 as a signal pressure for supplying fuel to the fuel cell 11;thus, the energy of the power storage unit 12 is gradually reduced.

Subsequently, in step S06, it is determined whether a value obtained bysubtracting the terminal voltage Vst of the fuel cell 11 from the outputvoltage Vfc of the fuel cell 11 is higher than a predetermined voltagedifference ΔV.

If the determination is “YES”, then the flow proceeds to step S07,wherein the current control process steps after step S05 are carried outby limiting the current output from the DC-DC chopper 17 a to a valuelower than the predetermined value.

In contrast, if the determination in step S06 is “NO”, the flow proceedsto step S08, wherein a transient control mode is set, that is, thecurrent output from the DC-DC chopper 17 a of the secondary prechargeportion 17 is set to a value corresponding to the amounts of hydrogengas and air to be supplied to the fuel cell 11. The series of controlprocesses are completed.

That is, for example, as shown in FIG. 5, when controlling the outputcurrent Ifc of the fuel cell 11 by the DC-DC chopper 17 a of thesecondary precharge portion 17, it is possible to adjust the timerequired for the output voltage Vfc of the fuel cell 11 and for theterminal voltage Vst of the power storage unit 12 to reach theequilibrium voltages (V_(MOT)≈Vst≠Vfc) by changing the duty ratio of theswitching command input into the DC-DC chopper 17 a.

As described above, according to the control device 10 for starting thefuel cell vehicle, at the time of starting the fuel cell 11, the currentis output from the power storage unit 12 through a resistor 16 c by theprimary precharge portion 16 disposed at the output side of the powerstorage unit 12, and it is possible to prevent generation of an in-rushcurrent, corresponding to a large current rapidly flowing in a capacitor(for example, an electrolytic capacitor as shown in FIG. 1), which isprovided in the control portion 23 of the PDU 14 or the air compressor15, or provided at the input side of the DC-DC converter 25.

In addition, after the load side voltage of the motor voltage V_(MOT)becomes approximately the same as that of the terminal voltage Vst, bylimiting the output current Ifc of the fuel cell 11 via the secondaryprecharge portion 17, it is possible to prevent a large current fromrapidly flowing to the power storage unit 12, whose terminal voltage Vstis reduced by supplying power to the auxiliary devices for driving thefuel cell 11 such as the air compressor 15, and, therefore, it ispossible to prevent an excessive reduction of the output voltage Vfc ofthe fuel cell 11 in the course of conversion of the terminal voltage Vstof the power storage unit 12 into an equilibrium voltage.

In addition, the use of the DC-DC chopper 17 a in the secondaryprecharge portion 17 allows for easy control of the output current ofthe fuel cell 11 by changing the duty of the pulse current input forcontrolling the chopping operation, and it is possible to reduce thetime for the output voltage Vfc of the fuel cell 11 and the terminalvoltage of the power storage unit 12 to reach an equilibrium voltage,while preventing an excessive reduction of the output voltage Vfc of thefuel cell 11.

Even when the difference between the output voltage Vfc of the fuel cell11 and the terminal voltage Vst of the power storage unit 12 is large,the use of the DC-DC chopper 17 a of the present embodiment is far moreadvantageous than the use of a contact point switch system such as theprimary precharge portion 16 for outputting the current through theresistor 16 c which switches the contact points to change the outputpath. This is because in the DC-DC chopper, there is no need to beconcerned about the malfunction of the switching device resulting fromarc welding of the contact points when releasing the contact points.

In the present embodiment, a chopper system using the DC-DC chopper isused as the current limiting circuit. However, the system for performingthe current limiting control is not limited to the chopper system, and avariant such as a transistor-type current limiting circuit, or adepletion-type FET system current limiting circuit can be used.

A described above, the first aspect of the present invention provides acontrol device for starting a fuel cell vehicle, and is capable ofpreventing a rapid reduction of the terminal voltage of the fuel cell byproviding a current limiting device for limiting output current at thetime of starting the fuel cell.

That is, it is possible to prevent an inflow of a large current from thefuel cell to the power storage unit whose terminal voltage has beenreduced by consumption of energy for driving the fuel cell. While thelimited current gradually charges the power storage unit, the terminalvoltage of the power storage unit and the terminal voltage of the fuelcell are gradually converted into an equilibrium voltage with respect toeach other. Thus, the evaporation of hydrogen or of the water content,or a decrease in the durability of the fuel cell can be prevented, sothat the control device of the present invention contributes tolengthening the service life of the fuel cell.

What is claimed is:
 1. A control apparatus for starting a fuel cellvehicle comprising: a fuel cell for supplying electric power to a load;a capacitor for assisting a supply of electric power to said load andfor storing generated energy by said fuel cell; a fuel cell drivingdevice for supplying reaction gases and for driving said fuel cell; anda current limiting device for limiting an output current from said fuelcell; wherein, at the time of starting the fuel cell, said capacitorsupplies electric energy to said fuel cell driving device and saidcurrent limiting device prohibits said fuel cell from outputting anoutput current until an output voltage of said fuel cell reaches apredetermined voltage, and wherein, after said output voltage rises tomore than the predetermined voltage, said current limiting device limitssaid output current of said fuel cell to below a predetermined currentvalue until a difference between said output voltage of said fuel celland a terminal voltage of said capacitor reaches a predetermined voltagedifference.